﻿#include<iostream>
using namespace std;
int main() {
	int a;
	cin >> a;

	switch (a) {
	case 1:
		cout << "1";
		break;
	case 666:
		[[fallthrough]];//c++17新特性，提示编译器跳过检测break
	case 777:
		break;
	}

	switch (2) {
	case 2:
		int b = 2;
		break;
	case 3:
		break;
	}
	//报错是因为case 2没有加括号，当case 3时int b的值在case 3中有效但没声明
}